Gas turbine engines include a compressor for compressing air, a combustor for burning fuel in the pressure of the compressed air and a turbine for providing power. The turbine of the engine comprises at least one rotor which is a rotatable array of radially aligned blades. Rotors are adapted to rotate when impinged upon by gases produced in the combustor of the engine. This rotation of the turbine rotors produces the thrust of the engine and the power to operate the compressor for directing compressed air into the combustor.
The efficiency of the turbine engine depends partly upon the angle at which the combustion gases approach the rotor. Thus, a nozzle, or an array of nonrotatable blades, is positioned in advance of each rotatable array of turbine blades. The nozzle changes the direction of the combustion gases to insure that these gases approach the turbine rotor blades at an angle that will insure most efficient operation of the engine.
Efficiency of the turbine engine also is directly proportional to the temperature of the combustion gases approaching the rotating arrays of turbine blades. Thus, greater engine efficiency is possible when higher temperatures can be employed. In most prior art gas turbine engines, the metallurgical characteristics of the engine components impose limits upon the engine operating temperatures. As a result, most prior art gas turbine engines have utilized a portion of the air compressed by the engine to cool portions of the engine that otherwise might be damaged by the high temperature combustion gases. This compressed air required for cooling otherwise would have been directed to the combustor to contribute to even higher temperature combustion gases, and hence even greater efficiency.
Several gas turbine engines have been manufactured in recent years which utilize ceramic components at locations subjected to particularly high temperatures. The ceramic components can withstand much higher temperatures than most metals. Consequently it is unnecessary to cool the ceramic components and it is possible to utilize combustion gases at higher temperatures. This reduction of cooling and the related increase in combustion gas temperature can result in improved engine efficiency.
One gas turbine engine which employs ceramic components is shown in U.S. Pat. No. 4,398,866 which issued to Hartel et al on Aug. 16, 1983 and is assigned to the assignee of the subject invention. U.S. Pat. No. 4,398,866 is directed to a gas turbine engine wherein a radially inner ceramic ring is disposed in juxtaposed relationship to the tips of a turbine rotor. An arrangement of two annular ceramic rings each of which is substantially L-shaped in cross-section is disposed adjacent to the inner ceramic ring and radially outwardly therefrom. The two L-shaped cross-section rings effectively entrap the inner ceramic ring. An outer metallic support holds the two L-shaped cross-section rings in proper relationship to the inner ceramic ring and the rotor during various conditions of operation. The entrapment of the inner ceramic ring is achieved through inclined adjacent surfaces which substantially insure the structural integrity of the ceramic members in the event of a crack therein. The metal members also can be provided with a preload biasing force to insure the proper relationship of the components during conditions when the combustion gases are not imposing forces upon the engine components.
Another engine employing ceramic components is shown in U.S. Pat. No. 4,008,978 which issued to Smale on Feb. 22, 1977. U.S. Pat. No. 4,008,978 includes an inlet turbine nozzle of cast ceramic construction. The nozzle includes a plurality of ceramic vanes extending generally radially between an annular ceramic base and an annular outer ring portion. The engine of U.S. Pat. No. 4,008,978 further includes ceramic rotors and stators disposed axially along the engine as well as ceramic shroud rings and tip shrouds. The various annular members all are circumferentially segmented to enable easy manufacture.
Other gas turbine engines employing ceramic components are shown in: U.S. Pat. No. 4,260,327 which issued to Armor et al on April 7, 1981; U.S. Pat. No. 4,365,933 which issued to Langer et al on Dec. 28, 1983; U.S. Pat. No. 4,273,824 which issued to McComas et al on June 16, 1981; U.S. Pat. No. 3,901,622 which issued to Ricketts on Aug. 26, 1975; U.S. Pat. No. 3,867,065 which issued Schaller et al on Feb. 18, 1975; U.S. Pat. No. 3,635,577 which issued to Dee on Jan. 18, 1972; U.S. Pat. No. 2,668,413 which issued to Giliberty on Feb. 9, 1954 and German Offenlegungschrift No. 28 31 547 which issued to Norton Company on Feb. 1, 1979.
Although most of the above identified references have the advantage of enabling higher engine temperatures and hence higher efficiency, it has been recognized that room for significant improvements still remain. For example, the turbine nozzle is subjected to higher temperatures than any of the downstream rotors or stators of the turbine assembly. Consequently it would be desirable to provide a nozzle formed entirely of ceramic material. Additionally, many of the known gas turbine engines with ceramic components utilize small, complex interlocking are sections to form the various annular members of the gas turbine engine. This use of short arc sections purportedly facilitates manufacturing. However, while these large number of sections may have overcome certain heretofore difficult manufacturing problems, they have created greater problems associated with the manufacture and assembly of a great number of parts. Most engines employing a large number of circumferential sections generally have not addressed the problem of certain portions of these segments cracking, breaking off and causing extensive damage to turbine sections downstream. Additionally, many of the prior art engines have not adequately addressed the problems associated with affixing ceramic components to adjacent metal components. The structures to accomplish these ceramic to metal connections have generally been very complex.
Accordingly, it is an object of the subject invention to provide a gas turbine engine having an improved ceramic nozzle assembly.
It is another object of the subject invention to provide a gas turbine engine having a nozzle formed from a relatively small number of parts.
It is an additional object of the subject invention to provide a gas turbine engine having a nozzle that can be easily assembly.
It is a further object of the subject invention to provide a gas turbine engine having a nozzle that can be securely and easily mounted relative to the metal engine components adjacent thereto.
It is still another object of the subject invention to provide a gas turbine engine having a ceramic nozzle assembly that is securely and nonrotationally mounted in the engine.
Another object of the subject invention is to provide a gas turbine nozzle that substantially prevents parts thereof from falling inwardly and into contact with other components of the engine.